Vacuum cleaners which use cyclonic separating apparatus are well known. Examples of such vacuum cleaners are shown in U.S. Pat. No. 4,373,228, U.S. Pat. No. 3,425,192, U.S. Pat. No. 6,607,572 and EP1268076. The separating apparatus comprises first and second cyclonic separating units through which incoming air passes sequentially. This allows the larger dirt and debris to be extracted from the airflow in the first separating unit, enabling the second cyclone to operate under optimum conditions and so effectively to remove very fine particles in an efficient manner.
In some cases, the second cyclonic separating unit includes a plurality of cyclones arranged fluidically in parallel. These cyclones are usually arranged in a ring extending about the longitudinal axis of the separating apparatus. Through providing a plurality of relatively small cyclones in parallel instead of a single, relatively large cyclone, the separation efficiency of the separating unit, that is, the ability of the separating unit to separate entrained particles from an air flow, can be increased. This is due to an increase in the centrifugal forces generated within the cyclones which cause dust particles to be thrown from the air flow.
Increasing the number of parallel cyclones can further increase the separation efficiency, or pressure efficiency, of the separating unit for the same overall pressure resistance. However, when the cyclones are arranged in a ring this can increase the external diameter of the separating unit, which in turn can undesirably increase the size of the separating apparatus. One proposal to increase the number of cyclones without correspondingly increasing the overall size of the separating unit is to arrange the cyclones into groups or banks of cyclones, one group being ‘stacked’ above the other group. Whilst this cyclone configuration benefits the size of the separating unit, it makes sealing the outlets of the cyclones challenging.